This invention relates to a charge transfer analog to digital converter circuit, and more specifically relates to a novel preamplifier using charge transfer techniques to permit the connection of a low output level sensor, such as a thermocouple, to an analog to digital converter circuit of the charge transfer type.
Control systems are well known, wherein the output of a sensor, such as a thermocouple is used as an input to the circuit. Such control systems may be used to control the operation of an appliance, and rugged and inexpensive thermocouples are used for this purpose. The drawback of such systems is that the thermocouple (or other sensor) produces a low level output signal which cannot accurately be converted by standard analog to digital converters without expensive preamplification. Particularly, when such signals are applied to standard analog to digital converters, the resultant output has a very low resolution. To overcome this problem, prior art control systems utilize stable, high gain d-c amplifiers to preamplify the sensor output before application to the analog to digital converter. Due to the stability and linearity requirements, prior art MOS amplifiers are unsuitable and the amplifier was usually formed using discrete and costly devices.